2400 33RD ST GEOTECHNICAL INVESTIGATION 2018-01-02 MF Import

' vehicles operating on the underlying fine-grained soils. Typically, the equipment will rut or 'pump' this soil causing difficulties in construction and the creation of a weak subgrade. • With the current design of excavating the stronger soil at the surface, the resistance of the soil to lateral earth pressure is quite low. • The results of the pore pressure dissipation test shown in Appendix D do indicate that the rate of water movement is rapid for a fine-grained soil. This compliments the original geotechnical report consolidation data that indicates the same. In areas where settlement will occur, the dissipation should occur quite quickly. Recommendations Based on the new data and analyses performed for this addendum, we shall answer the above questions in order. Pavement Issues • The existing pavements at or near the site are performing well because the pavement section in place is adequate for the traffic loading. The section is either 4 to 8 inches of asphalt concrete or 6 inches of concrete over 18 to 24 inches of compacted granular fill. This section rests on the underlying fine- grain soil that is not as dense nor will it support cyclic loads directly. • Based on the new data, it is apparent that an appropriate th;-kness of asphalt or concrete over a compacted soil thickness of 18 to 24 hes will support heavy traffic loading. This was the original design presented in the 25Aug99- geotechnical report. However, there are other possible approaches that do not require the over excavation and backfilling task; 1. Construct the new pavement section on top of the existing 18 to 24 inches of compacted soil currently on the site. We understand that this is not possible due to other critical design issues that require the lowering of the grade. 2. Place a non -woven gco-textile over the exposed subgrade after the design subgrade elevation has been reached. Then place the designed pavement section. • Based on the results of a meeting held at Inca's office on I6Dec99 including Ming Wang and Sandy Glover, it was decided to not over -excavate and replace 24 inches of soil but to use the geo-textile. Preliminary cost data indicated that the geo-textile approach was less costly to construct. • !due to this change in subgrade preparation, the pavement sections must be altered so only one type of base course crushed gravel material is used. This material must be spread out unto the fabric in one lift. The objective is to have no equipment driving on either the subgrade or the fabric until the crushed rock is in place and full thickness. Utilities that are deeper theri the fabric level should be placed prior to the fabric. The gco-textile should be Miriti 60OX or equivalent and the pavement section should be as follows; I. In auto parking lot areas; place fabric on proof rolled subgrade, then 8 inches of base course (1.25 inch minus) topped with 4 inches of asphalt. Gmteehnical, Tunncl and Environmental Engineers 3080 1256 Ace NE 11I,one (425) 969-5778 lidleme. WA 98W5 Page 3 Fax (425) 861-0677